By Pete O'Rourke - Follow me on Twitter @SkySportsPeteO

Campbell has found first-team opportunities limited at the Stadium of Light under manager Martin O'Neill this season.

The forward, who has scored one goal in 15 appearances, is out of contract at the end of the campaign and has been linked with a January move.

The 25-year-old had been tipped for a return to Hull, where he previously spent time on loan from boyhood club Manchester United, but it appears fellow Championship high-fliers Cardiff have joined the race for his signature.

Campbell joined Sunderland in 2009 after departing Old Trafford, where he came through the youth ranks.